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Re: st: spatial weights which also take into account time


From   Nick Cox <njcoxstata@gmail.com>
To   statalist@hsphsun2.harvard.edu
Subject   Re: st: spatial weights which also take into account time
Date   Thu, 31 Jan 2013 17:05:01 +0000

A very general answer is

1. Many programs support weights of various kinds.

2. If you want your weights to depend on several variables, that's
often fine: you just have to compute them.

3. The syntax is typically [<weighttype> = <exp>] so that the <exp>
can depend on several variables. Often it would be a product or a
dividend.

4. The general syntax (literally -syntax-) for checking weights and
the specific ways that weights are handled within a program should be
considered separate matters. (At the worst end, I've seen user
programs support specification of weights but then ignore them, it
being supposed by novice programmers that it's sufficient to allow
weights via a -syntax- statement.)

All that said, your specific problem sounds like a case for using an
-if- restriction, not more complicated weights, but I can't comment
authoritatively on -spwmatrix-.

Nick

On Thu, Jan 31, 2013 at 4:51 PM, Ben Hoen <bhoen@lbl.gov> wrote:

> I have been unsuccessful in my search this morning for a way to deal with
> both space and time (or for that matter any other variable other than space)
> in developing a spatial weights matrix.  ALERT: I am a novice - slowly
> learning - about spatial models.
>
> The k nearest neighbors options in some user written programs (e.g.,
> spwmatrix - SSC) allows me to limit the number of neighbors based on
> "nearness".  Alternatively I could use some cutoff distance (e.g., 1 mile)
> to limit the collection of "neighbors".  But in addition to distance I would
> like to use time to limit my data.  For example I have home transactions
> that I want to test for spatial autocorrelation between.  I concern myself
> with BOTH the k (e.g., 5) nearest neighbors that ALSO transacted within the
> previous year.  (I.e., using a transaction that occurred, for example, 10
> years later does not make sense, even if it is "nearest".)
>
> Are there any ideas out there for how to limit the data based on both space
> AND time in developing the weights matrix?
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